SAGT News

Rock around the General Cemetery - Saturday 17th March 2018 from 2.00 till 3.30 pm

No, not another pop festival among the tombs, but a peaceful walk around the other sorts of rock!
Discover how well (or how badly!) the Victorians selected and carved their tombstones
and how the memorials have fared since.

Let the stones teach you about the evolution of the Earth itself, and of the British Isles
in particular. No booking required. Children must be accompanied by an adult.

Meet at the Gatehouse of the Cemetery, Cemetery Avenue, off Ecclesall Road, S11 8NT.
Guide: Peter Kennett, Sheffield Area Geology Trust, in association with the Sheffield
General Cemetery Trust
(http://gencem.org/events/)
which invites a donation to the Trust.

Charter Square - posted 2 March 2018

Charter Square - general view of the new stonework

A highly metamorphosed xenolith in the dark Chinese "granite". The 1p coin is 2cm diameter

A cross-bedded sandstone from Hall Dale Quarry

Sheffield Council's Landscape Architects have continued their thoughtful use of natural
stone with the new work being installed in Charter Square. The general view shows the
paving in a range of pale-coloured Chinese granites, the bench seats and one of the sandstone
"monoliths". These large blocks are of Namurian age and come from the Hall Dale Quarry,
near Darley Dale, and some show cross-bedding and ironstone nodules. The seats are made
from pink and buff Stanton Moor Sandstone, with the legs of Stoke Hall Sandstone from
Grindleford. A dark "granite" from China is used for the kerbstones and many of these
display superb xenoliths of older rock fragments, highly metamorphosed by the heat of
the granitic magma. Some slabs have huge white feldspar crystals, which cooled from
the magma at a slower rate than the rest of the rock and so had more time in which to
crystallise.
Further work is planned in Charter Square, so keep your eyes peeled!

Match it! - posted 1 January 2018

SAGT is endeavouring to match some well-known Sheffield
buildings to the sources of their building stone. Here is one
in which we are confident, where fieldwork and archive research
have come together.
The former Sheffield Royal Infirmary, 1793, was built from sandstones
of the Loxley Edge Rock. Small quarries and worked blocks of stone occur
in the woodland below the scarp face of Loxley Edge (at Grid Ref
SK3105 9058; purple scale bar is 25cm).

Best minor fold? - posted 1 January 2018

Is this the best minor fold in Sheffield? (About 100m downstream of
Forge Dam at Grid Ref SK305850). The tape shows one metre. The fold
axis runs roughly parallel to the trend of the valley of the Porter
Brook, so could the fold be the result of earth movements or "valley
bulging"? Discuss!

19th Century ironstone mining legacy - 8 December 2017

Rows of mounds of shale spoil from individual shafts sunk to extract the Tankersley ironstone
seam (approx average depth 20m), viewed from the public footpath across Tankersley Golf
Course. These workings date from the early nineteenth century and the ironstone was smelted in
furnaces at the Thorncliffe works of Newton, Chambers & Co

Rock Oddity - 2 December 2017

1) linked impressions on a bedding surface forming an enclosed, globular shape, about 3cm
across, filled with matrix and shelly debris, having thin, elongate (segmented?) protuberances.
2) about 3cm away, is a curved depression of almost similar size.

In section it seems to displace the bedding surface below it, and may of course have nothing to do with 1)!

Fieldwork collaboration with University of Derby - 1 December 2017

Three Derby University geology undergraduates are undertaking their dissertation work
under the supervision of Dr Sian Davies-Vollum and in cooperation with SAGT, as follows:
Callum Moller and Jacob Dean are both studying the distribution and sedimentology of the
Greenmoor and Grenoside Sandstones in the Sheffield area from Graves Park in the south
to the Greenmoor area in the north. This work involves outcrop scale analysis as well
as hand and thin section petrographic descriptions. Once their analyses are complete
they will compare and contrast their results with previous work.

Danny Haywood is studying the geology of the Porter Valley area including Brown Edge
quarry. He is applying geological and geomorphological mapping to understand the
distribution of sedimentary rocks and is undertaking a detailed sedimentological
analysis of the outcrops at the quarry.

Notable geologists - latest update 1 December 2017

Silkstone Volcano - 29 November 2017

Small scale sedimentary structures

Not all volcanoes are big and dangerous. Sand volcanoes are centimetres high,
and produce sedimentary features that are even smaller. This one, at the
bottom of the Silkstone Rock, seems to have been formed when the weight of
overlying sediment caused the grains in the beds below to settle into a
tighter packing. This compaction displaced the water in those beds and bedding planes
upwards into a sand volcano. The sand bed above became fluid, and now is not
flat lying, but shows over-folds, rotors, and flame structures just above the
"throat" of the volcano.

One that got away - 19 November 2017

Rock Farm Barn

Rock Farm Barn sketch

SAGT got a call about a "strange rock in a barn wall". The photograph looked interesting,
but it was unclear, and by the time we got there the builder had concreted it. Luckily they are a
sharp-eyed bunch and we got a good description - and another photo.
There is a sharp, curving surface in an 80cm high vertical section, striking 215N (more or less!)
dipping to SE and disturbing and brecciating the Greenmoor Rock. To the west, 100m away, is a
large normal fault downthrowing SW and striking NW-SE. We're still working on it.

Site inspection visits near Rotherham - Thursday 16 November 2017

Four SAGT members made site visits to two designated RIGS (Regionally Important Geological Sites) in
Rotherham on Thursday. Both are abandoned historic quarries.

Great Bank Quarry

The rocks exposed at Great Bank quarry are the only outcrops within Rotherham district
of a thick bed of sandstone called the Dalton Rock. This sandstone forms a resistant
caprock bed on top of a long, thin, mesa-like hill that projects northwards towards
Dalton Parva because Dalton Brook has eroded a valley through its western side. Brecks
Lane runs along the top of the mesa and Dalton Parva is built on its northern tip.
The Dalton Rock has not been found underground in any colliery shafts or boreholes.
Cross-bedding measurements made by SAGT at Great Bank indicate that the river
which deposited the sand flowed unusually in a northwesterly direction at that point. The quarry
at Great Bank does not appear to have been worked since 1850.

Silverwood

The cliff-like rocks exposed at Silverwood were the result of excavations made in the
early twentieth century when the bottom of the brook was widened to accommodate railway
sidings associated with Silverwood Colliery. This site is the best of of three known
outcrops of a sandstone bed called the Ravenfield Rock in the Rotherham area. It is
also the highest sandstone bed of the Carboniferous Coal Measures preserved beneath
the Permian unconformity in this area. The basal contact between the sandstone and the
underlying mudstone rock is revealed along the base of the cliff, a feature which is not often seen.

Sheffield General Cemetery - 13 & 14 November 2017

Sheffield General Cemetery

A SAGT member led two groups of 30 Year 3 children from Greystones Primary School in
investigating the geology of gravestones in Sheffield General Cemetery on 13th and 14th November.

The Old Mines of Greystones Cliffe - Saturday 4 November 2017

Discussion of old bell pits in Porter Valley

A temporary exposure of an old mining gallery in an excavation for a new lamppost

Peter Kennett led a geo-walk on behalf of the Friends of the Porter Valley.
21 people attended the walk around the former mining area of the High Storrs Roughs
and Greystones Cliff on 4th November. The geology of the Porter Valley floor revealed
glimpses of Namurian and Westphalian sandstones, some of them cross-bedded and tilted.
A tight monocline exposed in the stream banks near Forge Dam is probably the result
of valley bulging. Duncan McLean identified fossil casts of Calamites roots, which
were found behind the former Leather Wheel dam.

Shallow mines for coal and ganister were worked from the 17th Century until the early
20th Century, with little modern evidence remaining, so the tour was embellished with
photographs and diagrams. However, the recent excavations for new lampposts (Now backfilled)
had revealed two coal seams and part of a mine gallery, still open, although dug in
heavy clay! Fragments of coal and dark shale were found in the mounds around the old bell
pits in the Roughs, so visitors felt that the interpretation was correct.

Survey of Permian rocks around Roche Abbey - 28 October 2017

SAGT conducted a preliminary field survey of several sites around Roche Abbey and the Maltby Dike
valley. This was needed because the information the SAGT database holds on these sites was over
10 years old, and because the Permian Limestones (Dolostones) are always interesting to see,
especially on a warm autumn day, in one of the strangest (but pretty) valleys in the area.
Oh, and there was a 12th century abbey lying about somewhere between the exposures.
These beds were all in the Cadeby Formation, and lie just above the basal unconformity, which is
nowhere exposed, sadly. They record events shortly after the Zechstein Basin flooded in over the
East England Shelf. Thick units of pisolitic beds alternate with a range of fine grained and
laminated limestones, with tantalising hints of burrows, and even one place looking suspiciously
like Hummocky Cross Stratification. There are patches of the Basal Permian Sands in the area,
but none at the sites visited.

A further visit is planned, but if you want to know more about the Permian in our area, go to the
Permian webpage